D-Link EBU-101-T2 single port PoE Power over Ethernet power injector base unit.
** MISSING Power Adapter **
What is it and what is it for?
This is a PoE power injector. As far as I can tell, you connect a standard Ethernet cable into one port (this goes back to the network) and another Ethernet cable (which goes to the device needing PoE) to the other port. The other connector is for the power adaptor.
What this means is that it turns a standard Ethernet connection into a PoE connection.